1. Technical Field:
The invention relates to an oil recovery process and more particularly to a process of preparing a polymer gel for oil recovery applications.
2. Description of Related Art:
Polymer gels have potential application to a number of oil recovery processes including cementing, fracturing and conformance improvement. Poor vertical conformance results from the vertical juxtaposition of relatively high permeability geologic regions to relatively low permeability regions within a subterranean formation. Poor areal conformance results from the presence of high permeability streaks and high permeability anomalies within the formation matrix, such as vertical fractures and networks of the same, which have very high permeability relative to the formation matrix. Fluids generally exhibit poor flow profiles and sweep efficiencies in subterranean formations having poor vertical or areal conformance. Poor conformance is particularly a problem where vertical heterogeneity and/or fracture networks or other structural anomalies are in fluid communication with a subterranean wellbore across which fluids are injected or produced.
A number of attempts to remedy conformance problems exist. U.S. Pat. Nos. 3,762,476; 3,981,363; 4,018,286; and 4,039,029 to Gall or Gall et al describe various processes wherein gel compositions are formed in high permeability regions of subterranean formations to reduce the permeability therein. According to U.S. Pat. No. 3,762,476, a polymer such as polyacrylamide is injected into a formation followed sequentially by a crosslinking agent. The sequentially injected slugs are believed to permeate the treatment region of the formation and gel in situ.
It is generally held that effective polymer/crosslinking agent systems necessitate sequential injection of the gel components followed by in situ mixing because gel systems mixed on the surface are difficult to regulate. Systems mixed on the surface often gel at an excessive rate, forming gel balls before they can effectively penetrate the treatment region. However, in practice, conformance treatments such as that disclosed in U.S. Pat. No. 3,762,476 using sequentially injected gel systems have also proven unsatisfactory because of the inability to achieve complete mixing and gelation in the formation. As a result, gels only form at the interface of the unmixed gel components and often in regions remote from the desired treatment region. Likewise, processes employing sequentially injected gel systems for cementing and fracturing applications have proven unsatisfactory because the resulting gels do not have sufficient strength and integrity to withstand the stresses encountered in oil recovery processes. Even when such processes are operable, the polymers commonly used with them are relatively expensive, which can render the treatments impractical from an economic standpoint.
A need exists for a gelation process which can produce a range of versatile gels having the desired predetermined strengths and integrities for conformance-improving, cementing, or fracturing applications. A need exists for a gelation process which can accomplish these objectives in a cost-effective manner.